It is the presence or absence of this additional mechanism that differentiates the two theories observationally 这个额外机制的显现与否,正是在观测上区分此两种学说的要件。
These additional mechanisms add powerful ways to add to or customize a type s functionality , but not without a significant cost 这些附加机制为添加或自定义类型的功能提供了功能强大的方式,但需要大量开销。